Antennas can be characterized by their far field gain patterns. Some antennas have complex mechanical feed structures that are time consuming to assemble and test (e.g. to determine antenna feed performance characteristics). Typically, a specialized antenna measurement facility is required to test an antenna and determine the performance of the antenna including the associate feed structure. One testing method is to use a near field antenna scanning system to collect data and then post process that data to characterize the antenna feed. This method has shortcomings in that it does not capture all of the radiated energy, requires specialized equipment and/or facilities and is not well suited to in-process testing (i.e. such specialized equipment and/or facilities are sometimes not well suited for testing of antenna subsystem (e.g. such as a feed assembly) during the manufacturing/assembly process.